How many litres of a 50% acid solution must be added to 30 litres of a 20% acid solution to obtain a 30% acid solution?
Correct answer D. 15 litres
Explanation
20% : 50% = (50 - 30) : (30 - 20) = 2 : 1. With 30 litres of the 20% solution, the 50% solution needed = 15 litres.
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